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JEE Main 2024
Inverse Trigonometric Functions
Inverse Trigonometric Functions
Hard

Question

For α,β,γ0\alpha, \beta, \gamma \neq 0, if sin1α+sin1β+sin1γ=π\sin ^{-1} \alpha+\sin ^{-1} \beta+\sin ^{-1} \gamma=\pi and (α+β+γ)(αγ+β)=3αβ(\alpha+\beta+\gamma)(\alpha-\gamma+\beta)=3 \alpha \beta, then γ\gamma equals

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Solution

Let sin1α=A,sin1β=B,sin1γ=C\sin ^{-1} \alpha=A, \sin ^{-1} \beta=B, \sin ^{-1} \gamma=C A+B+C=π(α+β)2γ2=3αβα2+β2γ2=αβα2+β2γ22αβ=12cosC=12sinC=γcosC=1γ2=12γ=32\begin{aligned} & \mathrm{A}+\mathrm{B}+\mathrm{C}=\pi \\ & (\alpha+\beta)^2-\gamma^2=3 \alpha \beta \\ & \alpha^2+\beta^2-\gamma^2=\alpha \beta \\ & \frac{\alpha^2+\beta^2-\gamma^2}{2 \alpha \beta}=\frac{1}{2} \\ & \Rightarrow \cos \mathrm{C}=\frac{1}{2} \\ & \sin \mathrm{C}=\gamma \\ & \cos \mathrm{C}=\sqrt{1-\gamma^2}=\frac{1}{2} \\ & \gamma=\frac{\sqrt{3}}{2} \end{aligned}

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